In the bowl of an electric mixer, beat the butter and 1 cup of the sugar until pale and fluffy, about 3 minutes. Add the egg and vanilla and beat on low speed until well combined. Gradually add the flour mixture, alternating with the milk, and beat on low speed until smooth. (Note: the batter will be very thick.)

Divide the batter evenly in the 18 prepared muffin liners.

Arrange the fruits on top so that they completely cover the batter.

Sprinkle the remaining 3 tablespoons of sugar over the fruits.

Bake for ten minutes, then reduce the heat to 325°F and bake until the muffins are lightly golden and a tester comes out clean, about an 20 minutes.